Fischell Department of Bioengineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/6628
Browse
3 results
Search Results
Item OPTIMIZATION OF DEDICATED BREAST COMPUTED TOMOGRAPHY: BOWTIE FILTER DESIGN AND OPTIMAL SPECTRUM ANALYSIS(2014) Kontson, Kimberly; Chen, Yu; Jennings, Robert J; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, researchers have been investigating the use of a new imaging modality called dedicated breast CT as a means of alleviating the problem of tissue superposition that comes from acquiring a two-dimensional image of a three-dimensional object in conventional mammography. Several groups have investigated the optimal spectrum for this new imaging modality using the dose efficiency as the FOM, but results are inconsistent. None of these groups have employed the use of bowtie filtration in their optimal spectrum studies. Given the right design, the inclusion of bowtie filtration will lead to improved dose efficiency as well as consistency in the metric independent of position in a given phantom. Bowtie filters can improve performance in several ways, including DR reduction, scatter reduction, patient dose reduction, and reduction of beam-hardening effects. In this dissertation, three different filter types with different choices for the tradeoffs between the performance improvements listed above are described. Examples of each type of bowtie filter are created for computational and Monte Carlo analyses, and two designs were fabricated for experimental analysis. Studies analyzing the material selection for each bowtie filter design and characterizing the scatter were also completed. Verification of the performance of the designs was done by calculating/measuring the HVL, intensity, and µeff behind the phantom as a function of fan-angle. The performance of the designs depended only weakly on incident spectrum and tissue composition. With various breast diameters, the calculated parameters varied the most, but the variation was substantially less than the no-bowtie filter case. For all designs, the DR requirement on the detector was reduced compared to the no-bowtie filter case. Simulation and experimental data showed that the use of our bowtie filters can reduce the peripheral dose to the breast by 61%, and provide uniform noise and CNR distributions. The best performing bowtie filter design was implemented in simulation studies analyzing the optimal spectrum through calculation of the dose efficiency metric. The results from this study show the improvement and consistency that can be obtained with the inclusion of the proper bowtie filter, and provide the research community with a methodology that will help lead to more consistent optimal spectrum results.Item TASK SPECIFIC EVALUATION METHODOLOGY FOR CLINICAL FULL FIELD DIGITAL MAMMOGRAPHY(2012) Liu, Haimo; Kyprianou, Iacovos S; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Purpose: The purpose of this dissertation is to evaluate the image quality of clinical Full Field Digital Mammography (FFDM) systems. This is done by evaluating image acquisition performance of clinical FFDM in a comprehensive way that accounts for scatter, focal spot un-sharpness, detector blur and anti-scatter grid performance using an anthropomorphic phantom. Additionally we intend to provide a limited evaluation of the effects that image processing in clinical FFDM has in signal detectability. Methodology: We explored different strategies and a variety of mathematical model observers in order to evaluate the performance of clinical FFDM systems under different conditions. To evaluate image acquisition performance, we tested a system-model-based Hotelling observer (SMHO) model on a bench-top system using a uniform anthropomorphic phantom for an signal known exactly background known exactly (SKE/BKE) task. We then applied this concept on two clinical FFDM systems to compare their performance. In a limited study to evaluate the effects of image processing in the detectability of FFDM, we implemented the channelized Hotelling observer (CHO) model on clinically realistic images of an anatomical phantom for an SKE/BKE task. Results: Even though the two systems use different detection technologies, there was no significant difference between their image acquisition performances quantified by the Contrast-Detail (CD) curves. We applied the CHO model to investigate the image processing algorithms used in GE Senographe DS FFDM system. For the particular SKE/BKE task with rotationally symmetric signals, the image processing tends to contribute to a non-significant reduction of system detectability. Conclusion: We provided a complete description of FFDM system performance including the image acquisition chain and post-acquisition image processing. We demonstrated the simplicity and effectiveness of both the MFHO and CHO methods in a clinical setting.Item Dose and image quality considerations in computed tomography(2011) Abboud, Samir; Kyprianou, Iacovos; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The increased use of Computed Tomography as an imaging modality is of concern because of the growing body of evidence linking radiation exposure to cancer incidence. However, a framework does not yet exist for balancing the immediate needs of the clinical task (image quality) with future risks due to the imaging procedure (dose). We developed a method to estimate the shape and thickness of materials yielding attenuation equivalent to that of bow-tie-shaped filters in clinical scanners. The results are especially useful for accurate modeling in Monte Carlo simulations of radiation transport. We then investigated measures of dose and image quality using both simulation and laboratory experimentation. We found that current measures of dose are robust under current clinical conditions. We also found that measures of image quality are object and task specific.